it's not a colony, there is no more Earth in Starfield, so that's all of humanity you see, not just America, hence the diversity.
Their diversity agenda kind of conflicts the lore, I think.
You can basically redo your character appearance anytime you want, and since it is a future it is not masked as a barber, surgeon or anything like that, but an in-lore service Enhance.
There are even quests about it and NPCs talking about using it etc.
And now the question, why the heck would half of NPCs look like wal-mart abominations when you can pretty get any body and looks you want?
I mean, it's pretty obvious that this body-positive bullshit would dissapear a minute after a service like this becomes available and affordable.